This invention relates to voltage control. In particular it relates to voltage regulators, and more specifically to the regulation of voltage in power supply systems.
In power supply systems it is conventional to have a power supply from a generating source fed to a substation transformer bank which may conveniently operate at distribution voltages such as 12 Kv. or 4 Kv. depending on the substation. From that station, power is passed through a regulator along a feeder to what is known as a feedpoint. The feedpoint is located reasonably adjacent in particular consuming areas and from that point on primary distribution is made to various areas, and it is transformed down to a consumer utilization voltage, for instance, 120/240 volts. Between the regulator and the feedpoint may be a distance of a mile or more and there is normally no load between the regulator and the feedpoint.
During any particular day the load from the feedpoint varies. For instance during the middle of the day when appliances and air-conditioners are switched on, the load increases. This tends to force the voltage lower. Contrarily at night as appliances are switched off and industry turns down, the load decreases and the voltage at the feedpoint tends to increase. These fluctuations in high and low voltage at the feedpoint are undesirable. When the voltage is low, appliances, and particularly those which are sensitive to voltage, for instance, computers and the like, will not operate as effectively as they should, and contrarily when the voltage is high a waste in power generation is taking place since this excess voltage is clearly unnecessary for the operation of the system.
Control of this voltage, to date, has been affected by regulators. The structure of these regulators is effectively a transformer winding system, the primary of the winding being at the bus or system voltage, and the secondary winding being connected to the feeder. Within the secondary is an additional winding with taps controlled by a regulator motor which is usually a split-phase single phase motor so that it can go forward or reverse. In this manner windings are added or removed from the secondary of the regulator thereby regulating the output voltage on the secondary, namely the feeder line.
In a common system, the regulator step winding is divided into 32 steps each representative of 5/8ths of a percent change in voltage and this quantitatively translates in a 120-volt system to each step change being 0.75 of a volt.
With the prior art, the voltage along the feeder and particularly at the feedpoint to consumers is controlled in a bandwidth of about 3 volts. It has not been desirable in the prior art to have a bandwidth any smaller than this since this would cause the regulator to step too often and thereby cause maintenance problems. Too tight a control, for instance 1.5 volts or less, in terms of the regulator performance, characteristics would cause overshooting and consequent hunting in the system. Thus, with the prior art systems the voltages in a conventional power supply system have varied in a range of 3 volts about the desired 120 volt supply. By having such a relatively wide bandwidth and the normally higher voltage during low load time, and normally lower voltage at high load times the regulators have reached levels which are undesirable for the aforesaid reasons.
Furthermore, with the prior art the broad bandwidth has been maintained by the utility to control the operations or step taken by the regulator to reasonable limits at the expense of tight voltage control at the feed point. In other words, it has not been easily possible with prior art systems to forcibly control feed point voltage within narrow limits which effects service to the customers, energy conservation, and system maintenance costs.